[4.x] Fix single digit month not working on whereMonth (#8697)

src/Stache/Query/Builder.php

@@ -190,7 +190,7 @@ protected function filterWhereMonth($values, $where)
                 return false;
             }
 
-            return $this->{$method}($value->format('m'), $where['value']);
+            return $this->{$method}($value->format('m'), sprintf('%02d', $where['value']));
         });
     }
 

tests/Data/Entries/EntryQueryBuilderTest.php

@@ -117,6 +117,11 @@ public function entries_are_found_using_where_month()
         $this->assertCount(3, $entries);
         $this->assertEquals(['Post 1', 'Post 2', 'Post 3'], $entries->map->title->all());
 
+        $entries = Entry::query()->whereMonth('test_date', 9)->get();
+
+        $this->assertCount(1, $entries);
+        $this->assertEquals(['Post 4'], $entries->map->title->all());
+
         $entries = Entry::query()->whereMonth('test_date', '<', 11)->get();
 
         $this->assertCount(1, $entries);